Current methods for assessing skeletal maturity in children of the United States are inadequate. The United States is a multi-racial nation, yet skeletal maturity standards are based on white children from many generations ago. It is the primary goal of the proposed study to rectify this disparity, and provide up-to-date race-specific modules to the FELS method for skeletal maturity assessment. With access to multiple existing radiographic collections of four different racial/ethnic groups nationwide, we will accomplish this goal through three specific aims. Aim 1 will determine differences between races in both the timing and tempo of skeletal maturity and its individual components. Aim 2 will re-calibrate the FELS method using data from contemporary children and provide new, user-friendly, free, and open source stand-alone and web-based computer programs with sex- and race-specific modules. Aim 3 will integrate two new personalized medicine outputs into the FELS program: maturation-category specific bone age, and conditional percentiles of skeletal age that can be used to predict the probability of catch-up maturation for a given child. The combination of these three aims will serve to benefit the treatment and clinical management of contemporary children nationwide.